Oxygen induced stacking faults (OSF) occur in the manufacture of silicon wafers. Measuring the OSF density is necessary for quality control in the manufacture of silicon wafers. Silicon wafers are used throughout industry, including by manufacturers of memory devices and microprocessors.
Known methods of measuring OSF density are limited to visual inspection by manufacturing operators. Visual inspection includes irradiating the surface of an oxidized and etched silicon wafer with a halogen lamp, spotting areas of haziness on the wafer, and measuring density with an optical microscope, either by photographing the location or directly through the optical microscope eyepiece, by counting the visible faults and multiplying by a factor based on magnification and area of image to determine density. Disadvantages of existing methods of measuring OSF density include the susceptibility to human error in visual inspection, the slowness of visual inspection by operators, and the lack of uniformity of visual inspection between operators. Other disadvantages include the need for a separate step in the manufacturing process for the visual inspection.
Heretofore, application of methods and articles for measuring OSF density by correlation to surface roughness measurement has never been performed. A method of measuring OSF density using methods and articles for measuring surface roughness of silicon wafers has never been performed. An automated method for measuring OSF density has never been performed. An automated method of measuring OSF density that does not rely on visual inspection by operators has never been performed. A method of measuring OSF density that uses existing inspection methods heretofore applied in other areas of inspection has never been performed.
EP 0702204 B1 (Aihara, et al) discloses a method of evaluating the crystal quality near the surface of a silicon wafer through microroughness analysis. The patent describes a relationship between microroughness and crystal quality and teaches that detection of the high sensitivity changes in the surface configuration of a silicon wafer provides a method of evaluating the crystal quality of silicon wafers. The invention defines crystal quality as "the surface configuration between each silicon crystal." The patent discloses that a method for evaluating crystal quality through microroughness analysis will replace the evaluation method of measuring dielectric breakdown voltage of an oxide layer. The patent neither identifies OSF density, nor relates crystal quality to OSF density. As such, the patent teaches away from the use of surface roughness measurement as a means to measure OSF density. The patent does not disclose replacement of the OSF density inspection quality control process.
Therefore, it is highly desirable to create an automated method of measuring OSF density. It is further highly desirable for creating a method of measuring OSF density that does not rely on visual inspection. It is also highly desirable to create a method of measuring OSF density that utilizes existing inspection methods heretofore applied in other areas of inspection. Potential customers for methods that meet these objects include silicon wafer manufacturers, memory and microprocessor manufacturers--any manufacturer that uses silicon wafers and has a need to measure OSF density on a wafer.